[VS-Mac]VisualStudio for Mac (Cocoa)でComboBoxのデータソースクラス

using System;
using Foundation;
using AppKit;

namespace MyTutorial_Combobox
{
    public class ComboBoxDataSource : NSComboBoxDataSource
    {
        private string[] _lines;
        #region Constructors
        public ComboBoxDataSource(string[] lines)
        {
            _lines = lines;
        }
        #endregion

        #region Public Methods
        public string ValueForIndex(nint index)
        {
            return _lines[index];
        }
        #endregion

        #region Override Methods
        public override nint ItemCount(NSComboBox comboBox)
        {
            return _lines.Length;
        }

        public override NSObject ObjectValueForItem(NSComboBox comboBox, nint index)
        {
            NSString value = new NSString("");
            if (index > -1)
                value = new NSString(_lines[index]);
            return value;
        }

        public override nint IndexOfItem(NSComboBox comboBox, string value)
        {
            return Array.IndexOf(_lines, value);
        }

        public override string CompletedString(NSComboBox comboBox, string uncompletedString)
        {
            foreach(string line in _lines){
                if(line.ToLower().Contains(uncompletedString.ToLower())){
                    return line;
                }
            }
            return "";
        }
        #endregion
    }
}

using System;

using AppKit;
using Foundation;

namespace MyTutorial_Combobox
{
    public partial class ViewController : NSViewController
    {
        public ViewController(IntPtr handle) : base(handle)
        {
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();

            string[] items = new string[] { "北海道", "青森県", "岩手県", "宮城県", "秋田県", "山形県", "福島県", "茨城県"
                , "栃木県", "群馬県", "埼玉県", "千葉県", "東京都", "神奈川県", "新潟県", "富山県", "石川県", "福井県"
                , "山梨県", "長野県", "岐阜県", "静岡県", "愛知県", "三重県", "滋賀県", "京都府", "大阪府", "兵庫県"
                , "奈良県", "和歌山県", "鳥取県", "島根県", "岡山県", "広島県", "山口県", "徳島県", "香川県", "愛媛県"
                , "高知県", "福岡県", "佐賀県", "長崎県", "熊本県", "大分県", "宮崎県", "鹿児島県", "沖縄県" };
            ComboBox1.DataSource = new ComboBoxDataSource(items);
            ComboBox1.Changed += (sender, e) =>
            {
                Label1.StringValue = 
                    string.Format("Event:Changed\nSelectedIndex:{0}\nShownItem:{1}\nStringValue:{2}\nIndexOf:{3}" +
                                  "\n\n直接入力した場合にはSelectedIndexは変わらないので要注意\nStringValueでデータが取得できる" +
                                  "\nindexはComboBox1.DataSource.IndexOfItem\n(ComboBox1, ComboBox1.StringValue)で"
                                  , ComboBox1.SelectedIndex
                                  , ComboBox1.DataSource.ObjectValueForItem(ComboBox1, ComboBox1.SelectedIndex)
                                  , ComboBox1.StringValue
                                  , ComboBox1.DataSource.IndexOfItem(ComboBox1, ComboBox1.StringValue));
            };

            ComboBox1.SelectionChanged += (sender, e) =>
            {
                Label1.StringValue = 
                    string.Format("Event:SelectionChanged\nSelectedIndex:{0}\nShownItem:{1}\nStringValue:{2}" +
                                  "\n\nStringValueは変更前の値なので要注意" +
                                  "\nComboBox1.DataSource.ObjectValueForItem\n(ComboBox1, ComboBox1.SelectedIndex)で取得"
                                  , ComboBox1.SelectedIndex
                                  , ComboBox1.DataSource.ObjectValueForItem(ComboBox1, ComboBox1.SelectedIndex)
                                  , ComboBox1.StringValue);

            };

        }
        public override void ViewWillAppear()
        {
            base.ViewWillAppear();
            this.View.Window.Title = "MyTutorial NSComboBox.DataSource";
        }
        public override void ViewWillDisappear()
        {
            base.ViewWillDisappear();
            //Windowを閉じる時にアプリも終了
            NSApplication.SharedApplication.Terminate(Self);
        }
        public override NSObject RepresentedObject
        {
            get
            {
                return base.RepresentedObject;
            }
            set
            {
                base.RepresentedObject = value;
                // Update the view, if already loaded.
            }
        }
    }
}